Method and apparatus for controlling the thickness of rolled strip material



1965 R. E. MARRS 3,170,344

METHOD AND APPARATUS FOR CONTROLLING THE THICKNESS OF ROLLED STRIP MATERIAL Filed Sept. 19, 1961 2 Sheets-Sheet 1 N I)? very 290/" Q N Poscoe f. War/'25 M s Q by 4 ///.'s A i-602W ey Feb. 23, 1965 R MARRS 3,170,344

METHOD AND APPARATUS FOR CONTROLL THE THICKNESS OF ROLLED STRIP MATE L Filed Sept. 19, 1961 2 Sheets-Sheet 2 In vent-or- Poscoe 5 Marv-'5 thethickness of the amount.

temperature of the material which occurlwhenfthe front end enters the rolling'pperation or when ithe'firear end fro'fn' a -furnace orroughing operation tothe final mill.

7 many other-conditions thatprodiice undesired variations in 'the thickness or "gage of the output strip. Theseinclude \hrolls and the niaterial; eccentricity in the'rollsfor variaf 'ess which employs successive'rolling operationsp-ifi it. 7 assumed-that the variation' in thewidth of thematerial is .fiow. ismeant that -the product of 'the thickness of the i uity of the material, itis not a true measure of the thickness when a hard spot of material is passing between the rolls.

masuredjby means' of X-rayfthickness gage afterit passesj through a rollorpressurepoingfand jthismeasureamountsitov an adjustmentiafter the'fact, I

V --isyimpbssibletoprovide continueds thicknss controlf' .14, whose position-is. regulated.- by meansofa meme;

United States Patent,

. 3,170,344 METHOD AND APPARATUS FOR CONTROLLING THE THICKNESS F ROLLED STRIP MATERIAL Roscoe E. Marrs, Schenectady, N.Y., assi'gnor to General Electric Company, a corporation of New York Filed Sept. 19, 1961, Ser. No. 139,193 7 Claims. (Cl. 80-35) My invention relates to methods and apparatus for re ducing the thickness of strip material by subjecting the, material to successive rolling operations, in each of which material is reduced a controllable In the reduction of the thickness of materials, such as, for example, reducing the thickness of a stripmaterial by passing itjthrough either a hot strip mill or a cold rolling millof thetandem type, one of the major problemsis maintaining the thickness of the final strip material at a constant gage value. The value of'constant gage material of desired'thickness is evident in that such material not only results in reduced expense for the manufacture of the material, but also provides reduced expense in subsequent manufacturing operations which use the material. on the other hand, in a thickness reducing operation such as a hot strip'r'nill; there are many factors which tend to promote variation in the thickness of the loutput' strip. These include decrease in temperature from the beginning to'the end of the strip materiahexcessive changes in the s romeachrollin'g stand. 'Additionalcontributing cold spots-in.the material, which areproduced n'd other supports usedfin conveying the material ln 'additionto the foregoing major lfactors, there -'are the millmspring or elastic constant of thefniill, wear' of the v working rollsfl variations in metallurgical. properties and 4t) inlfitheiwidth\oitirestrip:material; slippage between the tions in the speed of the rolls, and undesired irregularities in the screws .whichadjust the pressure on tli'e'ro'lls, such as irregularities in methods. of adjustment or 'ofrthelevel 5' Of'LTthELS CIGWSt's e desired" in a thickness reducing proc negligible,}is to maintain a constant' mass'flow of the material through-the successive rolls; By ,constantmass material vti'mes its speed remains constant for all rolls or pressure pointsthroughwhich the material passes. 4 v

.;In the past,r'n'any attempts have been made to achieve Q this result. For example, fone' systeml-for attempting -to obtain-uniform thickness of strip material measured the separatin'g force between rolls through" which the material} passes on the; assumption thatifQsuc'h separating force varied, the'nithe thicknessof fthe materialleavin'g there 0 ducing member or roll wouldvary'similarily; However, such systemfails to recognize the fact that, in rollingjstrip material, many times hard spots are encountered in such material, and since the separating force varieswith'du'ctil In; another arrangment, the thickness; of: the material is used: to .tcoritrol the force on the roll;". 'ljl ii s fro: fthatusually 'pair' o'f-rolls or pressure point and adjustingthe-pressure applied'tojthe material at such point'tom the tension in the material in advance.

sile 'stressin a strip'bf material being reduced r V p Rand the term "assfflowfto indieate lthegquantitylofma "terialipassingta i i i 'pressure' pointi isjlsed 0 indicate that point in the't ra vel o'f the' fstrip material twhichp ssure'fisj ppliedto t 11e" multistage rolling mill embodying my invention;

" tiensbr themilliof FIGURE Y G R 4 s asch'ematic View Cold m c ying my invention; and

3,1 79,344 Patented'Feb. 23, 1965 Furthermore, in such a system, although pressure is applied to the material at a number of spaced points in its travel, measurement by a thickness gage is made after the material passes through the first such point only, and the pressure at such firstpoint is adjusted accordingly. It has been found impractical for economic reasons touse an X-ray thickness gage after each such roll or pressure point to provide a continuous control of thickness.

It is an object of my present invention to provide methods and apparatus for reducing the thickness of strip material in which control of such thickness is obtained over the entire length of the strip. v

It is another object of my invention to provide'a new and improved method and apparatus for controlling the thickness of a strip material by maintaining constantthe; tension in such material as it is being reduced in thickness.

It is another object of my invention to provide a new and improved method and apparatus for reducing the' thickness of strip material which automatically corrects for changes or variations in the rolls used to reduce such material, including changes in the crown of the'roll or variations in roll dimensions because of changes in temperature. p i

It is still'anotherobject of myinve'nti on to provide a new and improved method and apparatus for reducing the 7 thickness of strip material by means ofa multistand roll-f 4 ing mill in which distribution of the loads on the motor thickness of output; strip material' which is subjected-to I successive rolling operations by maintaining substantially lco'n'stantf the mass flow of the jmaterialthrough each roll: v I ing operation, One of its features, consistsin sensingthef tension in such material inadv ance of its entry between a, v

used-herein,- the ;term. teiision is used. 0 1nd strip-by-a pairof rollsoriequiva j means'. P v v I e to b e' characteristic of p ula itr lt h lau my invention are set forth with pen claims; My inventionfitse lf, however, may best 1 begunderstood referencto the following description"; v

taken in connection Withthe accompanying, F ra'wings',

In the drawings," FIGURE its ,a schematic'viewiof a FIGUREZ is a perspective view'illustrating certai i JF RE 3 rer v i fr mo eden eel usedin the view of FIGURE 1; a five-standtandeni 5 FIGURE S isf a detail view of a'portion FIGURE 4.:

of this type, the strip 8 has-been"previously,broughtltd l, an approximate width a nd thickness'-.by.,a seriesot re; l

ducing stepsiin'a 'roughing mill. iEa'ch o the seeder-7.

comprises apair of ork rolls 9, .10.;driveri'by amot fo'r 11;

P'ressu'refpn Ithe materia between-the rolls 2,10 asserted;

by means of backup rolls,12,13' and a s'crewdown device v 1 5, whose operation, in turn, is regulated by means of a screwdown control 16 The initial pressure between the rolls 9, 19 or the opening between those rolls is adjusted customarily by utilizing a load cell 17, upon which pressure is exerted by backup roll 12.

In order to measure the thickness of the strip 8 after it passes through the rolls 9, of stand 1, I provide an X-ray thickness gage 18 which supplies control signals to screwdown control 16 over conductor 19. Such an X-ray thickness gage may be of a conventional type: for example, that disclosed in United States Patent No. 2,723,350-Clapp, and assigned to the assignee of this invention. As a result of the operation of the X-ray gage to control the pressureapplied on strip material 8 between rolls 9, 10 of stand 1, the material, after passing through these rolls, will be the thickness desired.

The pressures between rolls 9, 10 of the remaining stands 2- 7 are initially adjusted in the manner described in connection with stand 1 to provide a thickness of material emanating fromeach of these sets of rolls which is approximately that desired to give a desired thickness to the final or output strip which flows from rolls 9, 10 of stand 7. Between stands 1 and 7, it is desirable to reduce the thickness of the material in gradual steps to obtain a desired distribution of the loads on the driving motors of the stands. One measure of achieving this result is to obtain desirable limits of the tension, or tensile stress, in the material between different sets of stands.

' In' order to maintain tension in the material constant,- I provide tensioning devices 20 which 'may take, for

example, the form of upwardly biased rollers which engage the strip of material between each two sets of pressure rolls 9, 10. As will .be explained later, each of the tensioning devices 20 supplies a-signal over a conductor 21 to the screwdown control 22 of the next sue ceeding stand By controlling the position of the screwdown motors or drives 12 of each of these stands, each tensioning device -20'is.operative to maintain the tension in the strip 8 constant. In this fashion, despite tl occurrence of any hard Ispots in the strip 8 or any portionf of reduced thickness caused by elongation of the mate rial as it passes through a preceding set of rolls, each; I tensioning device 2tlis'operative to adju st the opening between: the sets of, work or pressure rolls 9, 10 of the next millstand toz maintain a constant tension inthe strip. In the case of the tensioning device 20 positioned be- The tensioning device 20 comprises a roller 34 carried; by arm 35 which is pivoted about an axis 36. Arm 35 carries a gear 37 which engages a cooperating gear 38. A motor 39, having a shaft 40 which carries gear 38,- operates through members 34-38 to provide a constant tension in the strip 8. The motor 39 preferably is a type MD motor conventionally used in rolling mills and frequently referred to as a torque motor. Any change in the position of roll 34 required to maintain such constant tension is operative to shift the position of the armature of motor 39 and, through a connecting gear box 41, the position of a control device such as, for example, a rheostat 42 of the tensiometer. Rheostat42, in turn, is connected in the circuit of the energizing fields 43, 43' of amplidynes 44, 44', whose armatures supply excitation current to the fields 45, 45' of two direct current generators 46, 46'. Direct current generators 46, 46', in *turn, supply operating voltages to screwdown motors 15, 15'.

FIGURE 2, which shows a partial view of the apparatus of stand 6, illustrates how the tensioning device 20 V the operation of a single stand is peculiar to stand 6. For all other stands, the tensioning device 20 which precedestlie stand is operative to supply only a control voltage to the screwdown motor, the speed of-eachother stand being regulated in a conventionalmanner in such mills to maintain'thedesired constant speed for the Work rolls of each-:stand. Obviously, this speed will-,bedif- .fereht for'each stand'in order that, in accordance; withmy invention, .the mass flow of ,materialnthrough'I-the successive stands remains constant. thethickfi s of H the materialisreduced as ittprogfs's'esthrough themill,

the speed oil-the Work rolls oieach .succe'edingstandis increased so thatthe product of the speed 656 ip times its, thickness' remains. substantially constaiit;

In FIGURE "3, 1 have shown arr-alternative arrange' V @ment for the gears 37, 38fofdFIGURE '2.' Thus,'i n

tween'st'ands 6 and 7, tliesignal'from that device,'-ratherv Q preset to the final thickness desired for the strip, I provide ,a 'second X-ray gage,24"positioned above the strip Should there be any deviation from the" 'than bein'g'operativeito control the pressure of stand 7,

is supplied over conductor 23 to driving motor 11 of standjfi to control the'speed of. rolls 9, 10 of stand 6.

Since the opening betweenrolls 9, 10 of final stand 7 is desired thickness, the signal supplied by X-ray thickness gage 24 modifies the. regulated speed of stand 7 so that the'resultant change in the actual striptension produces a corrective influence onthe strip thickness.

FIGURE 2 shows a perspective view .of a portion of the apparatus employed in myin'vention; This figure illustrates how backup roll 12 is supported ina-bearing block26 and pressure on backup 'roll 13 is exerted through bearing block 27 'and screw 14 which engages bearing block Screw 14'passes through a threaded support member Zllan'd atits upper end carries agear 2-9 which is driven by a worm or pinion 30 attached to the shaft of motor 15; Duplicate apparatus is provided for the two side siof the backup rolls 12;: 13,. the apparatus for FIGURE 3, the tension roll {34 is carrid by an arm 4'1 pivotedabout an axis 48., I Arm 47am the shaft 40 of motor v339 carry cooperating-nonlinear. gears.49', 50

which assist-to provideaconstant tension in strip 8 as 'roll 34 moves upwardly. Since drivingfmotor 39 isof the type which preferably supplies a constant torque, nonlinear'gears 49, 50 are, operative to supplyconstant torque to.roll 34. V 1 i In the operation ofvthe'apparatus of FIGURES 1-3,

.the initial opening between rolls 9, '10 of stand 1 is set according to, the thickness 'of the slab-or work piece which enters that stand, and the openings between the work rolls ofsucceeding stands-are .all adjustedbytheir separate screwdownmotors to gradually reduce the thick ness of the strip materialiso'that its ultimate'th'ickness 1s;of a desired value. 'In the, operation of thet -mill,-

my invention provides constant/tension in the strip-fie teri'al as it 'proceedsthrough the mill by adjusting theopenings of each successive set of work rolls 9, '10 in conjunctioriwith the speed'of' the motors driving those the left hand sides of these rolls being indicated by primed reference numerals; Drive motor'fl l supplies power 1 iv tothelwo'rk mus 91110 itihrqughi a g r box-31, and a pairf of a t 33 connected, respectivelyfwith the rolls 9, 1 r i I 'work rolls so'that the volume or mass flow delivered by each standto the nextsucceeding stand is substantially constant. In order to achieve this result, the tensioning device 20 senses or measures the amount of striptension and, in accordance with variations of that strip tension from a desrred. value, provides a signal to the screwdown;

motor of the next succeeding stand .to enlarge orre'duce the openingbetween the drive rolls 9, 10 of each-next succeeding stand to changethe tension in the strip be tween the two stands so that the tensioning device 're-. turns to its preselected position at which the-tension in the strip-is at desired value. Forexample, iftensioning.

device 20 between stands 3 and 4' rises vertically because of the lack of tension between these stands,v the device is operative to provide a control voltage to the screwdown motors 15, 15'.of stand 4 which momentarily reduces the pressure'on the strip as it passes between rolls 9, of stand 4, permitting .the material mass flow through stand 4 to increase until the tensionmg device, returns to its desired operative position.

When the thickness of the material which flows through stand 1 is constant as determined by X-ray thickness gage 18, and the relative speeds of each set of drive rolls are held constant and the positions of the tensioning devices 20 throughout the mill do not change, then the thickness of the strip material dehvered at the output of stand 7 is constant. When, however, a sect on of hardened material, caused, for example, by cooling produced by skids or other apparatus which con tacted the strip, passes through stand 1, it causes tensioning device 20 between stands 1 and 2 to lower and, in turn, bring the workrolls 9, 10 of stand 2 closer together to press or iron out the hard spots and restore the tensioning device 20 to its desired position. Each tenslonrng device 20 between the remaining sets of stands responds in a similar manner to this decreasing thickness caused by such a hard spot so that bythe time this seetlon of the strip material is delivered from stand 7, 1t 1s of a desired gage or thickness.

When an undesired tension is found to exist between stands 6 and 7, the signal produced by thechange in position of tensioning device- 20 is supplied over conductor 23 to drive motor ll'to increase'or decrease its speed so that thespeed of motor 11 responds. to the direction in which the tensioning device 20 s moved until a correct position of the device 2t) is restored.- If

a change in the speed 10f motor-drivingrolls-9, 1010f stand 6 causes the tensioning device 2 0 pos1t1onedjbe tween stands 5 and 6 to change its pos1t1on,.a voltage I is provided to the screwdo'wn motors of stand 6 to prosure at that point to maintain the'tension constant, the

' the 'strip of material leaves the number 6 stand, for

" tension jmay tend toincrease the gage. Therefore, it is a desirable toutilize the X raylthickness gage to. control "the thickness of the finalfproduct: Also; it is desirable that thejthicknessof thef strip of material,asitg leaves the number 6 standshould approach as nearly as possible 1 i the desired finalthiekness witha minimuni amount of tension ginthe strip vvheiritpasses-into thelaststand. v ;Another important advantage is that byptilizing' changes of tension in the stri p I the}pressureexerted at1th *next'succeeding-{pressure by .use of the signals obtained from" variations .in the r a i? ii nin "devices'iliij positions in any one of thePosiO g ptedrucq the material.- 1 v v I c 1 V i I} While I have shownand described particular embodimentsof my invention, it will, of course, be understood 7 that I do not wish to be ,hmited thereto since various changes and modifications may be made without depart- I ing from my invention, and I contemplate by the ap- QEIn FIGURE 4, I'havei'illustrated my invention as applied to a typical five-stand tandem 'cold nilli In such a mill,thestrip material 8 isinitial ly co led on a reel and, after reduction inthicknesa; isgwound on,a

winding reel. 61. Between the reels 6d," 611," thefstri'p material is subjected to successive pressureoperations,

staridco'mprising a pair or, work or pressurerolls 6'7,"

68 .upon which force'is exerted by' co operating backup rolls-69, 70. Pressure bu the upper backup roll 70 :is exerted by means of'ascrewdown motor .7 1. An X -raythickness gage 74 positioned. between "stands- 62, 63! provides a signal to control the pressure exerted by motor 71 on roll'70 of stand 62 to effect the initial reduction in the thickness of strip 8. A tensioning device 71 of stand 63 to adjust the force exertedon strip as it passes through stand;.63. Similar tensioning devices -motor 11 driving tens 7, as of stand s51 'Adadditiorial;

This signal in each of which the thickness o f the material is reduced, 4 These operations in the apparatus of FIGURE 4 are 7 Patent of the United States is:

X-ray thickness gage 74 positioned beyond the point of delivery from stand 66 provides a signal to .control the speed of the driving motor 11 of stand 66 for operation in accordance with principles discussed in connection with the operation of the apparatus of FIGURES 1-3.

FIGURES illustrates certain details of a typical stand of the apparatus of FIGURE 4. In this case, the tensioning device 72 comprises a fixed roller 75 and a pivoted roller 76, the latter being operative to move a core 77 relative to a coil 78 to provide a signal varyingflwith the position. of roller 76. This signal is, in turn, used to control theoperation of the screwdown motor and vary. the force exerted between the pressure. rolls 67, 68 of the succeeding. stand, as described in connection with the apparatus of FIGURE 4. While the tensiometer illustrated is of a well known type manufactured by the General Electric Company as type GO-4N, any other similar satisfactory tensiometer may be employedwith the apparatus of FIGURES 4 and 5.

In the operation of the apparatus for reducing the thickness of strip material embodying my invention, one important advantage is immediately apparent in that since the thickness of the material delivered at the output of the reducing apparatus is substantially uniform and kept closely to a desired finalthickness, the total length of strip obtained for a given amount of material is increased. Thus, by sensing the tension in the strip before it enters a pressure point and adjusting the pres;

thickness of the output strip is held substantially uniform, resulting in fewer over-"gage sections and greater total length of output strip for an input volume. V In the operation of the apparatus, when the end of example,*in the apparatuslof- FIGURE 1, a loss of strip material.- to 1 control point, my invention automatically corrects. for changes or; variations in the rolls usedftat the' p'ressu're pointjo pended claims to cover all such changes andmodifications as fall Within the 'true spirit' and scope'of my invention.

What I'claim as new anddesireto secure byiLettersl l in a rolling mill of the type stands through which a strip offmaterial to be reduced pair of opposed rolls rotating at'a predetermined speed, 5 the methodv of reducing material to a final thickness. which comprises passing the" material- -th1ough the stands ':in'successiomapplying pressure on the material in each stand, maintaining the speed of the rollsfin each stand atafixed predetermined speed, sensing the tension in the material before it enters a pair of stands and 'varying-the pressurefonthe'material at the -nextstand in '-;accordance with variations in" the tension in the ma 7 "72 are provided between the remaining. sets or stands. 1 Again, asinthecase ofthefapparatus'ofFIGURE 1,

\itheoutput' signal from' tensioning,.device 72; between standsf65 and 66 is'used to control the speed ofthe in thickness is'epassed, eachof the' stands comprising a terialbefore it enters the. stand' to maintain the mass flow of the'materialconstant.throughout the mill. 7

" ,stands="cforriprisinga pairlof opposed rolls operating :at

1 a'.;predeterminedspeed, the method of: reducing material,

having a plurality of 2. a rolling min consisting of a first sta rid,fa final stand, andja plurality of intermediate stands, each of the} being rolled to a final desired thickness while maintaining constant the mass flow of the material through the millcomprising passing the material through the stands in succession, applying pressure on the material in each stand, measuring the thickness of the material after it leaves the first stand and controlling the pressure in the first stand to obtain a desired thickness, maintaining the speed of the rolls in the intermediate stands at a fixed predetermined speed, sensing the tension in the material before it enters an intermediate stand and controlling the pressuretapplied to the material in such stand in accordance With the tension therebefore.

3. The process of claim 2 in which the thickness of the material is measured after it leaves the final stand and the speed of the roll in the final stand is varied in accordance with such measurement.

4. In a multi-stand rolling mill comprising a first stand, a final stand and a plurality of intermediate stands, each of the stands comprising a pair of material engaging rolls, the combination comprising an X-ray thickness 1 rolls of the following intermediate stand, whereby the thickness of a strip delivered by an intermediate stand varies with the tension in the strip in advance of such intermediate stand. I

5. In a-rolling'mill comprising a first stand, a final stand-and a plurality of intermediate stands, each' of the stands including a pair of material engaging rolls,

drive means for said rolls, and-a screwdown' motor for controlling the"pressure'exerteduby said rolls upon a strip of material passing therebetween, means for maintaining the speed of the rolls in the int'ermediate stands at fixed predetermined values, rneans for sensing the,

tension in a-:strip'being'rolledpriorto its passage toone of the intermediate stands, said tension sensing means being operative to control 'the serewdown motor and;the force between therolls 'of said one intermediate stand 7 whereby the thickness or, astripdelivered said, inter; mediate stand varies with the tension in [the strip'in advance of said stand. Y

30 References Cited by the Examiner V I UNITED STATES PATENTS 2,180,635 11/39 Iversen 80 35.1 2,287,851 6/42 Zeitlin 80--35.l 35 2,300,990 11/42 Stoltz s0 3s.1 2,345,765 4/44 Michael, s0 3'5.1 2,348,695 5/44 Reichert ..'8035.1 2,767,603 10/56 Rendel 8056.1 2,767,604 10/56 Whale'n' 80-561 40, 3,101,015 8763' out 1 Qs0-s5.1 v OTHER REFERENCES Control Engineering, September 1956, pages 116-117. f fAutomation, March 1956, pages 52-57. v 45 Wire, July 1961, pages 884, 926,927.

6. In a rolling mill comprising a first stand, a final stand, and a plurality of intermediate stands, each stand including a pair of material engaging rolls, drive means for said rolls, and 'a screwdown motor for controlling the pressure exerted by said rolls upon a strip of material passing therebetween, an X-ray thickness gage positioned between said first stand and the first of the intermediate stands for regulating the force exerted between the material engaging rolls of said first stand, means engaging the strip before it passes into an intermediate stand for sensing the tension in the strip passing through such intermediate stand, means responsive to said tension sensing means for controlling the screwdow'n motor of the next succeeding intermediate stand whereby the force exerted between the pair of rolls of the next succeeding intermediate stand. varies with'tension in the strip prior to its passage through the rolls of such intermediate stand, means for maintainingthespeed of the rolls of the intermediate: stands .at fixed predetermined values, and means for measuringithe thickness of the strip after it leaves said last stand, said last means being connected to control the speed of rotation of the rolls of said last stand.

7. In the rolling mill of claim 6 a penultimate stand, means for sensing the tension in a strip prior to its pass-- ing into the final stand and means controlled by said last means for controlling the speed of the pair of rolls of said penultimate stand.

STEPHENSON, Primary Examiner.

, LEON PEARQExuminer. 

1. IN A ROLLING MILL OF THE TYPE HAVING A PLURALITY OF STANDS THROUGH WHICH A STRIP OF MATERIAL TO BE REDUCED IN THICKNESS IS PASSED, EACH OF THE STANDS COMPRISING A PAIR OF OPPOSED ROLLS ROTATING AT A PREDETERMINED SPEED, THE METHOD OF REDUCING MATERIAL TO A FINAL THICKNESS WHICH COMPRISES PASSING THE MATERIAL THROUGH THE STANDS IN SUCCESSION, APPLYING PRESSURE ON THE MATERIAL IN EACH STAND, MAINTAINING THE SPEED OF THE ROLLS, IN EACH STAND AT A FIXED PREDETERMINED SPEED, SENSING THE TENSION IN THE MATERIAL BEFORE IT ENTERS A PAIR OF STANDS, AND VARYING THE PRESSURE ON THE MATERIAL AT THE NEXT STAND IN ACCORDANCE WITH VARIATIONS IN THE TENSION IN THE MATERIAL BEFORE IT ENTERS THE STAND TO MAINTAIN THE MASS FLOW OF THE MATERIAL CONSTANT THROUGHOUT THE MILL.
 4. IN A MULTI-STAND ROLLING MILL COMPRISING A FIRST STAND, A FINAL STAND AND A PLURALITY OF INTERMEDIATE STANDS, EACH OF THE STANDS COMPRISING A PAIR OF MATERIAL ENGAGING ROLLS, THE COMBINATION COMPRISING AN X-RAY THICKNESS GAGE MEANS POSITIONED BETWEEN SAID FIRST AND STAND AND THE FIRST OF THE INTERMEDIATE STANDS FOR REGULATING THE FORCE EXERTED BETWEEN THE MATERIAL ENGAGING ROLLS OF THE FIRST OF SAID STANDS, MEANS FOR MAINTAINING THE SPEED OF THE ROLLS IN EACH INTERMEDIATE STAND AT A FIXED PREDETERMINED SPEED, AND MEANS POSITIONED BEFORE EACH OF SAID INTERMEDIATE STAND FOR SENSING THE TENSION IN A STRIP PASSING THROUGH SAID INTERMEDIATE STAND, SAID TENSION SENSING MEANS BEING OPERATIVE TO CONTROL THE FORCE BETWEEN THE ROLLS OF THE FOLLOWING INTERMEDIATE STAND, WHEREBY THE THICKNESS OF A STRIP DELIVERED BY AN INTERMEDIATE STAND VARIES WITH THE TENSION IN THE STRIP IN ADVANCE OF SUCH INTERMEDIATE STAND. 